An image forming apparatus includes a photoconductor, a primary transfer belt, a primary transfer roller, and a secondary transfer roller. The image forming apparatus forms a toner image in the photoconductor, and transfers the toner image formed in the photoconductor to the primary transfer belt by the primary transfer roller. The image forming apparatus moves the primary transfer belt, and transports the toner image to a transfer nip formed between the primary transfer belt and the secondary transfer roller. In addition, the image forming apparatus transports a printing medium to the transfer nip. When the printing medium passes through the transfer nip, the image forming apparatus applies, to the secondary transfer roller, an electrical bias (a secondary transfer bias) for attracting the electrically charged toner on the primary transfer belt toward the secondary transfer roller. Accordingly, the image forming apparatus transfers the toner on the primary transfer belt to the printing medium.
In addition, in the image forming apparatus, after the toner image is formed, the printing operation may be interrupted. When the printing operation is interrupted, the image forming apparatus needs to remove the toner on the primary transfer belt in order to perform a next printing operation. Therefore, the image forming apparatus includes a belt cleaner that removes the toner from the primary transfer belt. The belt cleaner has a blade that is in contact with the primary transfer belt. The image forming apparatus moves the primary transfer belt, and transports the toner to a belt cleaning position where the primary transfer belt and the blade of the belt cleaner are in contact with each other. Accordingly, when passing through the belt cleaning position, the toner or other matters attached on the primary transfer belt are removed to a blade side from the primary transfer belt.
Further, when the image forming apparatus interrupts the printing operation, and transports the toner on the primary transfer belt to the belt cleaning position, when the toner on the primary transfer belt passes through the transfer nip, a bias (a cleaning bias) opposite to the forward bias is applied to the secondary transfer roller. Accordingly, the image forming apparatus prevents the toner from being attached to the secondary transfer roller from the primary transfer belt.
As described above, when the reverse bias is applied to the secondary transfer roller, paper dust accumulated near the secondary transfer roller is swept out toward the primary transfer belt by the reverse bias of the secondary transfer roller. The paper dust swept out to the primary transfer belt is removed by the belt cleaner. However, the paper dust has various sizes, and there is a possibility that not all paper dust is caught by the belt cleaner depending on the sizes of the paper dust. There is a problem when the toner and the paper dust are caught by the belt cleaner, but the toner and the paper dust may not be properly removed and remain in the primary transfer belt. This may cause image defects.